1. Field of the Invention
The present invention generally relates to a vehicle, including work vehicles such as an agricultural tractor, having a multiple gear ratio transmission and an operator actuated selector switch for selecting between manual or automatic speed control modes wherein the transmission is a variable transmission or has a finite number of gear ratios, and wherein in the automatic mode, an electronic controller automatically up-shifts the transmission and reduce the engine speed to maintain the desired vehicle speed and reduce fuel consumption when the load is reduced and automatically down-shifts the transmission and increase the engine speed when the load is increased. The present invention relates more specifically to such a vehicle having an automatic power management system, wherein the vehicle includes a device for determining a variable during automatic speed control mode to control the engine rpm and the transmission gear during automatic speed control mode, in which the variable is (a) the position of a selector switch, which is positionable in a field mode for operating the vehicle in a field, including tillage applications under changing load conditions, and a road mode for operating the vehicle during road hauling or transportation, (b) the position of a brake and ground speed, (c) vehicle slippage and ground speed, (d) an operator set maximum and minimum ground speed, (e) an operator set maximum and minimum gear setting, (f) system sensitivity, and/or (g) change in implement status.
2. Description of Related Art
The engine and transmission are the two primary components in the power train of a vehicle. The vehicle speed is determined mainly by the set engine speed (engine rpm or erpm) and set transmission gear and partially by the vehicle load. In manual speed control mode, the erpm is typically set by the erpm throttle lever. The gears are typically set by up/down-shift buttons. Power shift transmissions have fixed input/output ratios for each gear setting. To maintain a desired ground speed, the operator needs to adjust both the gear setting and the throttle lever position.
The drawbacks of manual vehicle ground speed control include it being impossible for the operator to detect and follow engine load constantly. Therefore, the vehicle will run with a preset erpm, which most often is different than the most efficient working point. Also, the operator has to set both erpm and gear to reach the desired vehicle ground speed, which can be arduous in some cases, such as during headland operation, during which the farm implements are turned around at the end of the field and multiple operations of implements are conducted at the same time.
Further, vehicle speed depends on the gear setting. Gear setting changes will cause the speed range to change. With a fixed erpm, such a gear shift or range change will cause a relatively high ground speed change.